// Protocol Buffers - Google's data interchange format
// Copyright 2008 Google Inc.  All rights reserved.
// http://github.com/jskeet/dotnet-protobufs/
// Original C++/Java/Python code:
// http://code.google.com/p/protobuf/
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
//     * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
//     * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
//     * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
using System;
using System.Reflection;

namespace Google.ProtocolBuffers.FieldAccess {

  /// <summary>
  /// The methods in this class are somewhat evil, and should not be tampered with lightly.
  /// Basically they allow the creation of relatively weakly typed delegates from MethodInfos
  /// which are more strongly typed. They do this by creating an appropriate strongly typed
  /// delegate from the MethodInfo, and then calling that within an anonymous method.
  /// Mind-bending stuff (at least to your humble narrator) but the resulting delegates are
  /// very fast compared with calling Invoke later on.
  /// </summary>
  internal static class ReflectionUtil {

    /// <summary>
    /// Creates a delegate which will execute the given method and then return
    /// the result as an object.
    /// </summary>
    public static Func<T, object> CreateUpcastDelegate<T>(MethodInfo method) {

      // The tricky bit is invoking CreateCreateUpcastDelegateImpl with the right type parameters
      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateUpcastDelegateImpl");
      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.ReturnType);
      return (Func<T, object>) closedImpl.Invoke(null, new object[] { method });
    }

    /// <summary>
    /// Method used solely for implementing CreateUpcastDelegate. Public to avoid trust issues
    /// in low-trust scenarios, e.g. Silverlight.
    /// TODO(jonskeet): Check any of this actually works in Silverlight...
    /// </summary>
    public static Func<TSource, object> CreateUpcastDelegateImpl<TSource, TResult>(MethodInfo method) {
      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method()
      // we'll call getter(x).
      Func<TSource, TResult> getter = (Func<TSource, TResult>)Delegate.CreateDelegate(typeof(Func<TSource, TResult>), null, method);

      // Implicit upcast to object (within the delegate)
      return delegate(TSource source) { return getter(source); };
    }

    /// <summary>
    /// Creates a delegate which will execute the given method after casting the parameter
    /// down from object to the required parameter type.
    /// </summary>
    public static Action<T, object> CreateDowncastDelegate<T>(MethodInfo method) {
      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateImpl");
      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType);
      return (Action<T, object>) closedImpl.Invoke(null, new object[] { method });
    }

    public static Action<TSource, object> CreateDowncastDelegateImpl<TSource, TParam>(MethodInfo method) {
      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method(y) we'll
      // call Method(x, y)
      Action<TSource, TParam> call = (Action<TSource, TParam>) Delegate.CreateDelegate(typeof(Action<TSource, TParam>), null, method);

      return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
    }

    /// <summary>
    /// Creates a delegate which will execute the given method after casting the parameter
    /// down from object to the required parameter type.
    /// </summary>
    public static Action<T, object> CreateDowncastDelegateIgnoringReturn<T>(MethodInfo method) {
      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateDowncastDelegateIgnoringReturnImpl");
      MethodInfo closedImpl = openImpl.MakeGenericMethod(typeof(T), method.GetParameters()[0].ParameterType, method.ReturnType);
      return (Action<T, object>)closedImpl.Invoke(null, new object[] { method });
    }

    public static Action<TSource, object> CreateDowncastDelegateIgnoringReturnImpl<TSource, TParam, TReturn>(MethodInfo method) {
      // Convert the reflection call into an open delegate, i.e. instead of calling x.Method(y) we'll
      // call Method(x, y)
      Func<TSource, TParam, TReturn> call = (Func<TSource, TParam, TReturn>)
          Delegate.CreateDelegate(typeof(Func<TSource, TParam, TReturn>), null, method);

      return delegate(TSource source, object parameter) { call(source, (TParam)parameter); };
    }

    /// <summary>
    /// Creates a delegate which will execute the given static method and cast the result up to IBuilder.
    /// </summary>
    public static Func<IBuilder> CreateStaticUpcastDelegate(MethodInfo method) {
      MethodInfo openImpl = typeof(ReflectionUtil).GetMethod("CreateStaticUpcastDelegateImpl");
      MethodInfo closedImpl = openImpl.MakeGenericMethod(method.ReturnType);
      return (Func<IBuilder>)closedImpl.Invoke(null, new object[] { method });
    }

    public static Func<IBuilder> CreateStaticUpcastDelegateImpl<T>(MethodInfo method) {
      Func<T> call = (Func<T>)Delegate.CreateDelegate(typeof(Func<T>), null, method);
      return delegate { return (IBuilder)call(); };
    }
  }
}
